Shielded electrical conductor construction and method of making the same



june 28; 1946. G, L Meeuw-CHAN SHIELDED ELECTRICAL CONDUCTOR CONSTRUCTION AND METHOD OF MAKING THE SAME Filed Feb. 24, 1945 Wffmgw Paentedfiuneis, 1946 SHIELDAED ELECTRICAL CONDUCTB CON- STRUCTION AND METHOD OF MAKING I THESARIE Geom L. Meeuwsen, nome, N. Y.. signor u Rome Cable Corporation, Rome, N. Y., a corporation of lew York Application February 24, 1945, Serial No. 579,622

1 8 Claims. This invention relates to radio-shielded electrical conductor and terminal or connector confstruction, more particularly of the -kind sometimes known as radio-shielded spark plug leads such as are employed in extending the electrical circuit connections from the manifold to individual spark plugs in internal combustion engines, and to a method of making the same.

One of the objects of this invention is to provide a practical and reliable radio-shielded spark plug lead construction that will dependably stand up under the widely varying conditions of practical use, that will be capable of advantageous manufacture and assembly, and that will effect reliable and long-lasting sealing against seepage thereinto of moisture, vapors, gases, or the like. Another object is to provides. practical and eilicient radio-shielded conductor and terminal con- Y struction. Another object is to provide a construction of the above character in which reliable leale-prooi junctions between terminal insulator i and filler compound in the shielding conduit may be achieved in a thoroughly practical manner well adapted for quantity production. Another object is to provide a construction of the abovementioned character in which insulating materials of diderent physical properties may be employed for the terminal insulator and for the insulating compound filling the space between the conductor and the shielding conduit in a manner so that the purposes and functioning of the one may not be detrimentally affected by the4 other. Another object is tov provide a construction ci' the above-mentioned character in which the terminal insulator is of a consistency or hardness to have resiliency appropriate to functionas a gasket, while the insulating or filler compound in the shielding conduit is of soit consistency, the two being sealed or joined togetherin such a manner that the gasket characteristics of the terminal insulator are not impaired by the softer material. Another object is to provide a simple, practical, and ei'licient method for making radio-shielded conductors with terminal insulators. Another object is to provide a method for dependably assembling and sealing a radioshielded conductorwith ller compound and a' terminal insulator having certain physical properties and functions different from those of the filler. all withoutimpairment of the properties of the one by the properties of the other. Another object is, in general. to provide an improved method and construction of the above-mentioned nature, and other oblects will be in part obvious or in part pointed out hereinafter.

iCl. 17de-76) tratively described herein, and the scope of the The invention, accordingly, consists in the features of construction, combinations of elements. arrangement s oi parts, and in the several steps and relation and order of each of the same to one or more of the others, all as will be illusapplication of which will be indicated in the following claims.

In the accompanying drawing, in which is shown, by way ci illustration, a preferred embodiment of the mechanical features oi my inven- 1 tion,

Fig. 1 is a central longitudinal sectional view, certain parts being shown in elevation and being partly broken away, of a radio-shielded conductor structure inone stage of its construction according to my method;

Fig. 2 is an elevation, partly in longitudinal cross-section, showing the construction in a suc Referring, nrst, tc Fig. 1, I preferably employ a, conduit, generally indicated by the reference `'character I0, which, for purposes of effecting radio-shielding, is metallic and preferably conrprises a flexible tube i0* made of helically wound, corrugated, strip sheet-metal, such as is shown in United States Patent No. 1,198,392, employins. if desired, suitable means, such as solder, for achieving improved tightness and strength, in

the manner shown and described in United States Patent No. 2,127,943, and preferably a covering lll of braided metal strands, as shown and described in United States Patent No. 1,340,818,

snugly envelops the exible tubing Il', being, of'

course, ilexible therewith. The ends of the conduit lli are received in suitable counter-bores il* of a suitably shouldered ferrule Il, to which they are secured in any suitable way to eil'ect a sealed connection, ior example, as by soldering. The ferrules- Ii have shoulders or iiangesfllb, with whlchengage the end shoulders I2. of nuts I2, internally threaded as at l whereby the respective ends of theconduit Il and related parts, later described, may be secured, for example, to

thcfeaternally-tbreaded shielding barrel or well parte throughout the several views of the drawi Il of a spark plug and'to a similarly externallythreaded cylinder, or well, or socket I4 associated with the manifold (not shown) in which the various spark plug conductors are contained. By means of the nuts I2, a mechanically secure connection to the parts Il and Il may be made, and, moreover, in co-action with other parts later described, dependable sealed junctions can be effected-all while achieving, also, a desirable quick detachability of the lead and terminal structural unit. l

Extending within the conduit IU, and suitably insulated therefrom, is a conductor i8, vhich is preferably flexible and, hence, may b e a stranded conductor; by way of the conductor I8, the high potential energy required to energize the spark plug is to be conveyed, and to insulate the conductor I8 from the radio-shielding metal parts of the conduit Ill I prefer to employ an in sulatlng covering I1 about the wire i8. and this insulation i'l may be of any desired or suitable construction or composition, or of combinations o1' insulating compositions or elements, preferably adequateI to dependably insulate the wire IB for the voltage of the energy it is to carry, with usual or appropriate margins of f safety. The wire IE extends preferably coaxlally of the conduit I0, which contains a suitable insulating compound I8 which can. if desired, be of a dielectric strength such as to provide for the adequate insulation of the wire I8 from the conduit l independently of the insulating covering or sheath I`I which, in such case, need not be ernployed. if desired, in so far as certain features of my invention are concerned. 'Ihe compound Il may be of any desired composition or material, preferably relatively flexible, and where the insulation I1 about the wire IB is omitted, the consistency of compound I8 is preferably such as to coact in maintaining the conductor substantially coaxially within the conduit Ill, or any other known means may be employed to maintain substantial coaxial relation.

With the insulating sleeve Il about the wire IB, however, many advantages are achieved; for example, precise coaxial relation need not be provided for; the compound I8 can, desirably, be'

of more advantageous consistencies, preferably relatively soft or ilowable, and thus better achieve, particularly when under compression, a more efilcient and more reliable filling ofV all of the space within the conduit I U and about the insulated conductor IS-I'I, and thus better guard against corona effects and against Possible dielectric breakdown.

Any suitable means may be employed to inject ,the insulating compound Il into the space between the conductor and the internal walls of the conduit, as by injecting a suitable quantity thereof upon completion of the assemblage ofthe ferrules and nuts to the conduit In, and. by means of the nuts. suitable connection may be made to any suitable apparatus for injecting the material II.

Having injected a suitable quantity -of the I compound Il into the space between the conductor and the conduit walls, the compound Il being in suitable plastic condition and being, illlltrtively. made up of any suitable uncured rubber-like material, such as natural rubber, any of the synthetic rubbers, or the like, each suit ably compounded, such of the compound Il as Projects beyond the outer ends of the ferrules II is removed or cleaned olf, so as to leave the end boundary of the material Il substantially alom a plane indicated at IB-all substantially as indicated in Fig. 1-the filler compound il being preferably compounded, in known manner, as by adding suitablev ingredients or fillers thereto, so that, uponl the application of heat to cure it. it swells or expands in substantial or appropriate extent and so that, upon completion of the cure. itis preferably not hard or rigid, but has sutilcient softness to be adequately flexible so as to bend with the bending of the conduit l0, as may be necessary.

Since the steps of my method and structural features according to my invention may be em ployed to construct the insulating terminal at each end of the conduit I0, it will sunlce to describe in detail the steps and apparatus, and the parts employed, with respect to one end of the conduit lll. The conductor i5, as shown in Fig. l, projects beyond the end of the conduit I0 throughout a length commensurate with the length of the insulated terminal structure to be employed, and, where the conductor i8 has an insulating jacket I1 thereabout, the jacket II is stripped from the extreme end portion of the ductor I6, thus to bare enough of the wire i8 to permit the application and connection thereto of any desired form of contact or terminal.

Onto the projecting length of conductor I now sleeve an insulating bushing or sleeve, generally indicated by the reference character 2| `the sleeve 2i is to coact with the nut 'I2 and ferrule Il to achieve a sealed junction with the spark plug well, or manifold cylindrical housing Il or I4 of Fig. 4, and, hence, is provided with an outwardly-projecting, annular sleeve, flange, or shoulder 2|l which lies against the end face iI of the ferrule shoulder IIb, by which it is tightly seated and compressed against the part I3 or I4 (Fig. 4) when the nut I2 is screwed home, the annular shoulder 2| e thus serving as a gasket. Bushing 2| is, therefore. preferably made of a relatively hard and toughl though still resilient, material and, illustratives, may be made of any suitable rubber-like material, such as natural rubber, synthetic rubber, or the like, compounded in known manner to give the desired hardness with the desired resiliency when subjected to an appropriate cure, usually by heat treatment, and the bushing or terminal insulator 2| is prefer ably premolded and cured, in any suitable way. before it is sleeved onto the conductor and brought into interrelation with the ferrule II.

The ferrule II and the terminal insulator 2l are shaped to provide coacting engaging surfaces which are proportioned to present large and rapidly increasing areas of contact for a given rate of movement of plastic material radially therealong, in comparison to the substantially fixed relationship of areas of contact between the bore 2| b of the terminal insulator 2| and the surface of the conductor structure IB-I'I within the bore, for the same rate of movement of the same plastic material therealong. For example, the

- engaging surfaces of the ferrule II and of the insulator 2i that lead to the gasket flange 2l* are made of progressively increasing radius, so that the areas thereof increase at a greater rate than does the radius along which the flow of Vplastic material, tending to escape from within the conduit I0, tends to move, the area increasing with the square of the radius. This relalationship can be achieved in any suitable way.

I ample, from the annular face II'J of the ferrule shoulder IIb, surface IIc presenting a rapidly increasing area with increase in radius, I may provide a surface I Id joined to the surface I I= of the shoulder II which forms the annular seat vwithin which to receive the ends of the conduit parts Iii=I and Ib, in turn joined by the external face I ig of the shoulder I if. One or more of the faces iid, I I, and IIg may be frusto-conical, and, by way of illustration, face IId is so shown; surface Iig may be cylindrical and surface II", if not frusta-conical, may. lie in a plane at right angles to the axis of the ferrule. In making up the 'insulating sleeve or bushing 2i, it is provided the surfaces IIe, iid, IIe, and IIS, respectively.

of the ferrule II, when the sleeve ZI is sleeved onto the conductor Il---i'i and seated in the feri rule II, as shown in Fig. 2.

matches the radius of the conductor structure I8I'l, provision being made for sufficient clearness to make for ease of sleeving of the insulator 2i onto the conductor structure, and the latter and the bore 2ib thus provide engaging or juxtaposed cylindrical surfaces of substantially the same radius.

The extreme inner end portion of the insulator 2I, with its end face 2|', is thus exposed to the insulating compound I8 .that fills the space between the conductor and the conduit I0, the

end face 2|# engaging and abutting against the l being provided with companion mold cavities l 22-22 shaped so as to snugly accommodate and envelop not only the yinsulator 2|, but also the shoulder Ilb of the ferrule Il, the nut I2 being sleeved away from the ferrule so as not to in- `2o The radius of the bore 2|b substantially' age take place, the material i8, in whole or in part, envelops the gasket flange 2I, and may even be forced further onto and along other external faces of the terminal insulator 2l. Were such leakage allowed to take place-and it has beeny impossible, according to prior practices, to prevent it-the nal structure is defective and becomes a reject, because, in curing the compound I3 to the desired extent, that is, to the desired softness, yieldability, or resiliency, those portions of the compound that have leaked onto the gasket flange 2I become united to it during the cure and the `flange 2i", of relatively hard or tough consistency with such resiliency as is intended forgood gasket connection, has its sealing or gasket actionv modified, usually erratically or irregularly, by the soft compound from the filler I8 that-becomes united to its external surfaces.

According to my invention, however, material of the'compound or filler i8 is precluded from4 insulator with respect to those of the ferrule and with respect to the possible paths along which the pressure of the filler material I8' tends to force or flow the compound. Thus, considering terfere with the engagement of the mold sections about the ferrule shoulder or flange IIb.y Any suitable means, such as dowel pins and holes, indicated at 23, may be employed to coact with the ferrule shoulder to align the mold sections as they are assembled about the ferrule part and the insulator 2I and brought together into the position shown in Fig. 3, whence the mold sections are secured together by any suitable clamping -means (not shown), and, with the other end of the shielded conductor structure likewise fitted with a cured, premolded insulator 2l and a sectional mold M, the complete entity is ready to be subjected to treatment to cure the filler compound I8 and to effect union thereof with thel pacting itself tightly and snugly against and about the conductor and also against the interior surfaces of the conduit I0; the hydraulic forces or pressures within the material IB are, however,

. also exerted against the end face of each of the terminal insulators 2l, but. the latter are tightly heid against their respective ferrules II by the molds M, the mold cavities of which are preferably so proportioned, particularly in those portions that accommodate the gasket fiange 2l* Figi 2, the fluid or plastic compound I8, under the pressure that it exerts, enters the narrow space between the bore 2 Ib and the surface of the conductor I6-II, and commences entry into whatever available space exists betweenthe annular surfaces IIz and 2If, both portions or streams being under the same pressure. portion that is forced along the bore 2|h meets with substantially uniform resistance, for the surfaces which it contacts (the bore 2 Ib and the con- -ductor snugly fitted therein) present the same lradius progressively increases along the stepped or zigzagged surfaces above described. Along this path, therefore, flow or movement is slower by far than along the path provided between the bore and the conductor, for a given quantity has to be spread over far greater contacting surface As a result of these relative coactions, the com` pound of the filler material I8 isprevented from reaching the gasket flange 2 I and from affecting its gasketing action, for the lesser resistance along That the path between the bore surface and the conductor permits more ready flow therealong, and the path along the bore functions in effect as a relief chamber or reservoir to receive material of the filler compound I8 that is forced out of the conduit Il), receiving it in suflcient measure -so that, aided by the increasing resistance and surface areas provided by the other path, the softer compoundY does not reach any surface of the gasket flange 2|.

Upon completion of cure, the relatively hard terminal insulator 2| and the relatively soft filler I8 are securely united to each other at the places where they have been brought into engagement, and the compound i8 becomes also united to the insulatingiacket I1, where one is employed, and is of a material such as those mentioned above that can be united together by vulcanization.

Upon completion of the cure, it being noted that any suitable form of contact terminal 25 may be assembled in any suitable Way to the end of eachconductor IE and terminal insulator 2| before the mold sections are assembled thereto, the mold sections are removed, and the completed structure is ready for installation in the manner above described, and as is better shown in Fig. 4,

where the nuts I2 are shown threaded onto the casing or well parts |3-I4 to compress the gasket flanges 2|* securely in sealing relation between the ferrules and the parts |3 and I4, respectively. In such sealing relation and action, it is only the cured material of the terminal insula- 8 mechanical working of the compound, as on mill rolls. Additions, during mechanical working, of oils, such as on oil of petroleum base, or of other suitable oleaginous substances which become Welll and highly dispersed throughout the material, may also be employed to materially increase the swelling characteristics, and,4 when employed, they have the additional advantage of plasticizing the compound and acting as a lubricant, to'

v characteristics.

tors 2|, specifically appointed, as above mentioned, for gasketing action, that effects the desired sealed relationships; the sealing flange in` each case has a uniform sealing action, being unaffected or uncontaminated by the soft, cured filler IB, the characteristics of which are appropriate for coaction between the conduit and `conductor and other parts, but are not appropriate to take part in a gasketing or sealing action.

Were the sealing flange to be contaminated, in while or in. part, as by leakage above mentioned, dependability onpermanency of seal would not be achieved and, instead, rapid failure would result at the point or points of contamination, it be ing understood that the sealed connection sometimes has to withstand substantial pressures, such, for example, as could be caused by leakage of high-pressure gases from the engine cylinder through the spark plug connection thereto.

As labove indicated, the filler |8 and the material of the terminal insulator 2| may be compounded out of any suitable insulating materials and ingredients, all for the purposes above described. Illustratively, and preferably, neoprene is employed for both, the compounding thereof being suitably or appropriately varied according to the respective characteristics desired for the filler IB and terminal insulators 2|. Whatever materials are employed, such as those earlier above mentioned, the respective compounding thereof for the filler |B and for the terminal lnsulators 2| may be effected, in any known manner, to give the filler IB, when cured, a Shore durometer reading on the order of |5 and a Shore durometer reading for the material oi. the insulators 2|, when cured, on the order of 65. Where substantial swelling of the filler I8 during cure is desired, suitable ingredients are added in the compounding thereof to cause materially greater swelling thereof during heat treatment than it might normally have, and also some control of the factor of swell may be effected by correspondingly controlling the extent and character of It will thus be seen that there has been provided in this invention a radio-'shielded conductor and terminal insulator construction and method of making the same in which the various objects above noted, together with many thoroughly practical advantages,v are successfully achieved. The construction is thoroughly dependable and ofl uniform action, and it will be seen that the method can be reliably carried out in practice with the attainment of consistent results conducive to quantity production.

As many possible embodiments may be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinaboveset forth, or shown in the accompanying drawing, is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a method of preventing contamination of the gasket-forming portion of an external terminal insulator by the vulcanizable insulating compound within the conduit of a radio-shielded lead that has fittings at an end thereof that comprise a ferrule that is in fluid-tight connection with the conduit and that has an annular face against which to receive a gasket, the steps which comprise forming a surface on the ferrule that extends in increasing radius from an internal portion thereof to said annular gasket face, placing a conductor within the conduit with a portion projecting beyond said ferrule, filling the space between the conduit and the conductor with a vulcanizable insulating compound that is componded to expand upon heat treatment, premolding out of suitable insulating material and curing to thedesired hardness and resiliency a terminal insulator with an annular gasket portion to overlie said annular ferrule face and with a surface of increasing radius to mate with said ferrule surface and with a bore to receive said projecting portion of the conductor, sleeving the terminal insulator onto the projecting portion of the conductor and bringing together said surfaces of increasing radius with said gasket portion overlying said annular ferrule face, subjecting Ithe assemblage to heat treatment to cure and expand said insulating compound and join it to said terminal insulator, and during heat treatment holding the parts together to hold said mating surfaces of increasing radius against material separation whereby they offer increasing resistance to movement therealong of compound under pressure and thereby preventv compound from reaching said gasket portion of the terminal insulator.

2. In a method of preventing contamination of the gasket-forming portion' of an external terminal insulator by the vulcanizable insulating compound within the conduit of a radio-shielded lead that has fittings atan end thereof that comprise a ierrule` that is in fluid-tight connection with the conduit and that has an annular face against which to receive a gasket, the steps which comprise forming a surface on the ferrule that extends in increasing radius from an` internal portion thereof to said annular gasket face, pleeing a conductor within the conduit with a portion projecting beyond said ferrule, filling the space between the conduit and the conductor with a vulcanizable insulating compound that is cornpounded to expand upon heat treatment, sleeving onto the projecting portion ofthe conductor a premolded terminal insulator that has an annular gasket portion to overlie said annular ferrule face and a surface of increasing radius to mate with said ferrule surface and a bore to receive said projecting portion of the conductor, subjectingl sistance to movement therebetween of compound under pressure, thereby y preventing compound from reaching said gasket portion of the terminal insulator.

3. In a method of preventing' contamination of the `gasket-forming portion of an external 'ter-v minal insulator by the vulcanizable insulating compound within the conduit of a radio-shielded l lead that has fittings at an end thereof that comprise a ferrule that is in huid-tight connection with the conduit and that has an annular face against which to receive a gasket. the steps which comprise forming an annular surface on the ferrule that extends in increasing radius from an internal portion thereof to said annular gasket face, assembling to the ferrule andthe c'onduit a terminal insulator that has an annular gasket portion overlying said annular ferrule face and an annular surface of increasing radius to substantially mate with said ferrule surface and a bore therethrough, a conductor within the conduit and extending through said bore. and a heat-curable annular gasket face, a sleeve-like terminal induit and through said sleeve-like terminal ininsulating compound within the space between the latter is prevented from reaching said lgasket portion of the terminal insulator.

4. A radio-shielded lead with terminal gasketforming insulator comprising a tluid-tight radioshielding conduit having a ferrule in huid-tight connection therewith at an end thereof, said ferrule having an annular gasket face' and having an annular surface of increasing ,radius extending from an internal portion thereof to said sulator of cured. relatively rigid, insulating material extending from said ferrule and having an sulator, and a cured, relatively flexible, insulatn ing compound within said conduit and about the conductor therein and integrally united to the material of said terminal insulator under conditions of pressure of the compound and of interengagement of said'annular surfaces to resist such extent of movement of compound during cure along said annular surfaces as would cause itfto reach and contaminate said gasket- Vforming annular portion of the terminal inferrule. aconductor extending within said conduit and through said sleeve-like termineraisulator, and a cured. relatively flexible, insulating compound within said conduit and about the conductor therein and integrally united tothe materialof said terminal insulator under conditions of pressure of the compound and of interengagement of said annular surfaces to resist such extent of movement of compound during cure along said annular surfaces as would cause it to reach and contaminate said gasket-forming annular portion of the terminal insulator. at least a portion of the length of any space between the conductor and the bore of said sleevelike terminal insulator, from the ferrule end thereof. containing, and being sealed by. cured compound that is forced thereinto under pressure during cure. f

. '6. In a method of preventing contamination of the gasket-forming portion of an external terminal insulator -by the vulcanizable insulating compound within the conduit of a radio-shielded lead that hag-nttings atan end thereof that comprise a ferrule that is in fluid-tight connection with the conduit and that has an' annular face against which to receivea gasket, the steps which comprise forming a surface on the ferrule that extends in increasing radius from an internal portion thereof to said annular gasket face. placing a. conductor within the conduit with va portion projecting beyond said ferrule, filling the space between the conduit and the conductor with a vulcanizable insulating compound that is compounded `to expand upon heat treatment. premolding out of suitable insulating material and curing to the desired hardness and resiliency a terminal insulator with an annular gasketportion to overlie said annular ferrule face and with a surface of increasing radius to mate with said ferrule surface and with a bore to receive saidproiecting portion of the conductor, sleeving the terminal insulator onto the projecting portion of the conductor and bringing together said surfaces of increasing radius with said` gasket portion overlying said annular Ierrule i'ace, applying a removable mold about the terminal insulator, securing it in relation to the ferrule to cause the mold to press and hold the terminal insulator axially inwardly of the terrule and thereby hold said mating surfaces of increasing radius against material separation, and

subjecting the assemblage 'to hcat treatment to cure and expand said insulating compound and join it to said terminal insulator. whereby iiow along said mating surfaces of compound being cured is limited as to distance of iiow against reaching and contaminating the annulargasket portion of said terminal insulator.

- GEORGE L; MCCUTCHAN. 

